1. Field of the Invention
The present invention relates to an aperture stop changing device for a camera. More particularly, the present invention relates to an aperture stop changing device for a camera having a simple structure, and also in which performance of a taking lens can be free from being influenced by the relevant elements for the aperture stop changing.
2. Description Related to the Prior Art
A lens-fitted photo film unit is a single use camera pre-loaded with photo film. Various mechanisms and elements in the lens-fitted photo film unit are simplified for the purpose of lowering the manufacturing cost. The lens-fitted photo film unit includes a shutter unit which a single shutter blade is biased in a closed position, and is knocked instantaneously toward an open position so as to take an exposure by opening and closing a shutter opening. In addition to the shutter unit, the lens-fitted photo film unit is provided with an aperture stop changing mechanism for the purpose of adjusting an exposure. An aperture changing plate of the aperture stop changing mechanism includes a stop-down opening, is movable but is different from the shutter blade. A photometric value or brightness is measured, according to which the aperture changing plate is changed over to change the aperture stop.
The aperture changing plate is movable between first and second positions, and when in the first position, sets the stop-down opening in the light path, and when in the second position, sets away the stop-down opening from the light path. Control of a solenoid causes the aperture changing plate to move, to change over an aperture stop. A photoreceptor is provided, and started upon depression of a shutter release button to detect an amount of object light. The solenoid is actuated by evaluating the object light amount. Therefore, it is possible to adjust an exposure even by use of a simple construction.
To reduce the manufacturing cost, the lens-fitted photo film unit is a structurally simplified product even in relation to a taking lens. Generally, the taking lens is constituted by one or two lens elements 20. Specifically, the type of the taking lens having two lens elements is advantageous, as effective in compensation for aberrations. Behind the taking lens is disposed a preset open aperture defining an open aperture in the lens-fitted photo film unit. A lens holder having a holder barrel portion is disposed on a front side of the preset open aperture. A first one of the lens elements is disposed on the rear side, and has a large diameter. A second one of the lens elements is disposed on the front side, and has a small diameter.
If the lens-fitted photo film unit having the taking lens of the two-lens-element type is provided with the aperture stop changing mechanism as described above, it is preferable to dispose the aperture changing plate between the lens elements, because of structures of elements near the end holder, and because high quality can be obtained and the camera should be compactly designed. The stop-down opening moves in a path and settable even to the front of the taking lens. If the aperture changing plate is inserted between the lens elements, it is likely that an end or tip of the aperture changing plate contacts and interferes with a lens surface to scratch or damage the same. It is also conceivable to dispose members for keeping the aperture changing plate positioned in the optical axis direction to avoid interference with the lens surface. However, this raises the number of the required parts, and is inconsistent to reducing the product size. This is not preferable due to those problems.
In view of the foregoing problems, an object of the present invention is to provide an aperture stop changing device for a camera having a simple structure, and also in which performance of a taking lens can be free from being influenced by the relevant elements for the aperture stop changing.
Another object of the present invention is to provide an aperture stop changing device for a camera in which an aperture changing plate can be positioned to move on a suitable plane, and can be prevented from interference with a lens surface.
In order to achieve the above and other objects and advantages of this invention, an aperture stop changing device for a camera is provided. The camera includes a preset open aperture for introducing object light to photo film, and a taking lens disposed in a light path of the object light, and having at least one lens element. In the aperture stop changing device, an aperture changing plate includes a stop-down opening having a small diameter, is disposed close to the taking lens, is movable between a small diameter position and a large diameter position, wherein the stop-down opening, when the aperture changing plate is in the small diameter position, is set in the light path for stopping down the preset open aperture, and when the aperture changing plate is in the large diameter position, is set away from the light path. A spacer is secured to a partial section of a peripheral portion of the taking lens, for defining a passage gap or cutout at a remaining partial section of the peripheral portion of the taking lens, the passage cutout allowing passage of the aperture changing plate moving between the small and large diameter positions.
The camera is a lens-fitted photo film unit.
Furthermore, a guide projection portion is formed to project from the peripheral portion of the taking lens toward the aperture changing plate, for contacting the aperture changing plate being moved, to regulate the aperture changing plate in an optical axis direction of the taking lens.
Furthermore, a lens holder is disposed behind the taking lens, for supporting the taking lens.
The guide projection portion is a ring-shaped ridge.
Furthermore, a retention plate is disposed in front of the taking lens, for securing the taking lens to the lens holder. A first retention portion is formed with the lens holder or the retention plate. A second retention portion is formed to project from a peripheral edge of the taking lens, fitted on the first retention portion, for retaining the taking lens on the lens holder or the retention plate.
Furthermore, a holder barrel portion is formed to project from a front surface of the lens holder, and fitted on the peripheral edge of the taking lens. A passage cutout is formed in the holder barrel portion, for allowing the aperture changing plate to move in and out.
Furthermore, a ring-shaped outer ridge is formed to project backwards from the retention plate, fitted on a peripheral edge of the holder barrel portion, for positioning to the lens holder.
The first retention portion is a retention cutout formed in the outer ridge, and the second retention portion is a retention projection.
Furthermore, a biasing mechanism biases the aperture changing plate to the small diameter position. A stopper portion is disposed in a moving path of the aperture changing plate, for contacting the aperture changing plate moved by the biasing mechanism, to keep the aperture changing plate from moving beyond the small diameter position.
Furthermore, a ring-shaped first positioning ridge is formed to project backwards from the retention plate, disposed inside the outer ridge, for pushing the peripheral portion of the taking lens.
Furthermore, a ring-shaped second positioning ridge is formed to project from a front surface of the taking lens, fitted on the first positioning ridge, for positioning the taking lens behind the retention plate.
According to a preferred embodiment, the spacer is a spacer projection formed to project from the lens holder toward the taking lens.
The aperture changing plate is disposed between the taking lens and the lens holder, the guide projection portion projects from a rear surface of the taking lens, and the spacer projection has a height equal to or more than a height of the guide projection portion.
Furthermore, a ring-shaped positioning projection is formed to project from a rear surface of the taking lens, and fitted on the spacer projection.
According to another preferred embodiment, the at least one lens element is at least first and second lens elements. The aperture changing plate is disposed between the first and second lens elements, the spacer is sandwiched by partial sections of peripheral portions of the first and second lens elements opposed to one another, and the passage cutout is defined between remaining partial sections of the peripheral portions of the first and second lens elements.
The second lens element is disposed in front of the first lens element, and the guide projection portion projects from a front surface of the first lens element.
Furthermore, a holder barrel portion is formed to project forwards from the lens holder, and fitted on a peripheral edge of the second lens element. A passage cutout is, formed in the holder barrel portion, for allowing the aperture changing plate to move in and out. A retention notch is formed in the holder barrel portion. A retention projection is formed to project radially from a peripheral edge of the spacer, fitted in the retention notch, for retaining the spacer on the lens holder.
Furthermore, a ring-shaped flare stopper is disposed close to the first or second lens element, for blocking light traveling away from the light path of the object light, to prevent flare.
The flare stopper is disposed between the aperture changing plate and the second lens element, for regulating the aperture changing plate with the guide projection portion.
The flare stopper contacts the aperture changing plate moving between the small and large diameter positions, for regulation in the optical axis direction.
Furthermore, a support pin is formed to project forwards from the lens holder, for supporting the aperture changing plate in a rotatable manner. The lens holder and the retention plate are disposed to cover a moving path of the aperture changing plate between the small and large diameter positions.
The aperture changing plate has a driven end. Furthermore, a solenoid has a plunger slidable between first and second positions. A transmission mechanism is connected between the plunger and the aperture changing plate, has a driving end movable into and out of a moving path of the driven end, wherein the driving end, if the plunger is in the first position, is away from the driven end for setting the aperture changing plate in the small diameter position, and if the plunger is in the second position, pushes the driven end for setting the aperture changing plate in the large diameter position.
Furthermore, a photometric unit measures object brightness. A control circuit controls the solenoid according to comparison of the object brightness with reference brightness, to set the solenoid in the first position if the object brightness is equal to or higher than the reference brightness, and to set the solenoid in the second position if the object brightness is lower than the reference brightness.
Furthermore, a first bias member biases the aperture changing plate toward the small diameter position. The transmission mechanism includes a stopper lever, having first and second ends, the first end being secured to and moved by the plunger, being in a third position when the plunger is in the first position, and being in a fourth position when the plunger is in the second position. A transmission lever is movable between fifth and sixth positions, has a third end and the driving end, the third end being movable into and out of a moving path of the second end, wherein the third end, when the stopper lever is in the third position, is retained in the fifth position, to set the aperture changing plate in the small diameter position, and when the stopper lever is in the fourth position, is allowed to move to the sixth position. A second bias member biases the transmission lever toward the sixth position, to set the aperture changing plate in the large diameter position.